The invention relates to a process for preparing organosilanes.
EP 1130023 discloses the preparation of organosilyl-alkylpolysulphanes of the general formula (R1R2R3Si—R4—)2Sq from the organosilylalkyl halide of the general formula R1R2R3Si—R4—X. The reaction is performed by initially charging elemental sulphur and the organylalkyl halide in a polar organic solvent and adding anhydrous or virtually anhydrous ionic sulphide to this suspension. Owing to the proneness of the Si-alkoxy bonds of the organosilylalkyl halide to hydrolysis, the ionic sulphides must be anhydrous or virtually anhydrous.
EP 1700861 discloses the synthesis of sulphur-containing alkoxysilanes using hydrous sulphurizing reagents in alcohol. When different raw materials are used, great differences are found in the monomer content of the resulting polysulphidic alkoxysilanes. A reliable, homogeneous product quality on the industrial scale cannot be achieved in this way. In addition, the use of four solids in the known process is disadvantageous for the industrial scale.
WO 2008025580 A1 discloses preparing sulphur-containing alkoxysilanes of the general formula [R(R)(R′O)Si—R″—]2Sm, wherein the alkali metal hydroxide content of all feedstocks must be <0.44% by weight.
Disadvantages of the known processes are either the use of anhydrous or virtually anhydrous starting materials or, in the case of hydrous starting materials, the strong dependence of the product properties on the raw material properties, especially the proportion of alkali metal hydroxides. In the known processes which use hydrous sulphurizing reagents, the use of more than 4 raw materials is undesired. Moreover, the metered addition and the use of alkali metal sulphide hydrate as a sulphurizing raw material is problematic, since solid alkali metal sulphide hydrates, as a result of the preparation, may contain relatively large amounts of alkali metal hydroxides. A low content of (mercaptoorganyl)alkoxysilane in the end product is desired.